1. Field of the Invention
The invention relates to an antenna device that is able to change its directivity.
2. Description of the Related Art
In an existing art, an antenna device called an ESPAR antenna is known as an antenna device that is able to change its directivity. For example, Japanese Patent Application Publication No. 2001-24431 (JP-A-2001-24431) describes the antenna device. The antenna device described in JP-A-2001-24431 has such a configuration that a plurality of passive elements are located at a quarter wavelength distance from a feed element and then a variable reactance element is connected to each of the passive elements. The directivity of the antenna device may be changed by varying the reactance value of each variable reactance element.
However, in the antenna device described in JP-A-2001-24431, the interval between the feed element and each passive element needs to be set to a quarter of wavelength, so it is difficult to reduce the size of the antenna device.